A variety of high-strength low-alloy steels typically of the SAE 4100 series are in extensive use for fabricating seamless casings and tubing for use in oil and gas well operations because of their excellent yield strength properties. During recent years, the necessity of increasing the depth of oil and gas wells in order to increase the production of crude oil and natural gas has occasioned problems in the use of such low-alloy steel tubular products due to sulfide stress-cracking as a result of their exposure to appreciable quantities of hydrogen sulfide at such increased depth in further combination with the increased tensile stresses imposed on the tubular products. The premature fracture of tubular components as a result of sulfide stress-cracking or hydrogen embrittlement has been particularly pronounced in some of the deep oil and gas well formations in the Louisiana and west Texas oil fields.
Because the susceptibility of low-alloy steels to stress corrosion cracking is dependent to a large extent upon the tensile stress present at the surface of the tubular product in contact with the hydrogen sulfide containing corrosive media, it has heretofore been proposed to alter the specific alloy chemistry and/or the proportions of the specific alloying constituents present in such low-alloy steels to provide an improvement in their yield strength, as well as an increase in their resistance to sulfide stress-cracking. Unfortunately, many of the new low-alloy steels proposed have been unsatisfactory from a commercial standpoint due to their increased costs, as well as requiring sophisticated fabrication techniques in lieu of conventional manufacturing processes normally used for producing casing and tubing of similar type.
In lieu of alterations in the specific chemistry of such low-alloy steels, it has also been heretofore proposed to apply various plastic and metal coatings or liners to the inner surfaces of such tubular products, providing thereby a barrier layer to protect the underlying steel structure from sulfide stress-cracking and/or hydrogen embrittlement. A composite tubular product of the foregoing type is disclosed in U.S. Pat. No. 2,982,360 in which a nickel-copper alloy liner is applied to the inner surface of a high-strength low-alloy steel so as to provide a corrosion-resistant barrier to inhibit sulfide stress-cracking of the steel component. While composite tubular products of the foregoing type have met with some success, the combined cost of the relatively expensive corrosion-resistant liners and the fabrication of the composite tubular products has detracted from their widespread commercial adoption.
The present invention overcomes the problems and disadvantages associated with tubular products of the types heretofore known by increasing their resistance to sulfide stress-cracking employing a relatively simple low-cost temper-stressing under controlled conditions, whereby the net tensile stress in the surface exposed to the corrosive liquids in service is appreciably reduced.